As I now have a Speidel Braumeister with amazing temperature stability, I can now also control the boil intensity (the temperature can be set to +100C). And so I was wondering what the latest insights are wrt rolling boils. I checked Kunze (v3) and he states that there is (was in the early 2000s) a tendency to reduce the boil intensity. If too many proteins are precipitated, this will have a negative impact on foam retention. Also, boiling too intensely will increase thermal stress.
Any thoughts on this? Where’s the evidence for us homebrewers?
In this interview Bamforth talked pretty extensively about how many larger scale breweries were not built to allow volatiles to escape efficiently during the boil and thus problems arose. I really think this is a non-issue for most homebrewers using kettles who are getting at least a good turnover of the liquid surface (rolling). I don’t think “jumping out of the pot” is necessary at all at the homebrew scale. I never worry about it - particularly because my 10 gallon pot is relatively wide and thus I get even better evaporation.
What is the deal with “thermal stress?” The last time I checked boiling wort was a liquid without feelings and without a metabolism.
I thought that lowering the boil rate in commercial brewing systems was driven by energy savings, which conceivably can be very substantial for a big operation. Could be entirely wrong on this point.
I suppose that the temperature of boils can be “considerably” higher than 100 *C if the kettle is deep enough, which is not a concern for homebrewers. For grins, I looked at a steam table. The boiling point of water/water at the bottom of 15-16 ft of water/wort is 232 *F, which could be a concern for commercial brewers.
Based on the evaporation percentages that pro systems produce and the percentages we homebrewers often experience, it’s my opinion that we homebrewers typically boil too hard and have too much exchange with the atmosphere…which results in too much evaporation.
Yes, the wort needs to be moving during the boil to help extract the elements from our hops and to expel undesirable elements from the wort. But we don’t need the wort to be leaping from the kettle throughout the boil duration. I’ve gone to partially covering my kettle to help reduce the exchange with the atmosphere. In addition, I limit the boil vigor to the point that I can see that the wort is moving trub and hop particles throughout the kettle. The other thing I do at the end of the boil is to increase the vigor to try and expel any DMS that might have accumulated in the early boil. It seems to be working, but without comparative trials, its just conjecture on my part.
Boiling too hard, just wastes energy and you end up with a lesser volume of more concentrated wort. Since you can’t produce kettle caramalization at boiling temps, that argument seems dubious to me. I think that perception that brewers say they achieve is just the result of the more concentrated wort.
My spreadsheet is structure so that you can pick boil off rate and boil time from a drop down. Changing them changes my preboil volume requirement and subsequently my sparge volume estimate.
I then adjust my hop times and amounts to compensate. I like short boils because I don’t have a dedicated brewing fridge for storing things like yeast and hops. I do small batches so I try to use all of a 1 oz. package of hops if I can for one batch.
It stands to reason that you should take anything anyone says with a fair amount of skepticism until you’ve tried it for yourself!
That last line was more of a reference to the fact that I don’t own the Kunze text and it hasn’t been widely read and digested among the brewers here.
If you read the reference it doesn’t account for that bit of process in the authors brew days. Basically, I’m not sure of the context.
Until I have read that passage in the text and understand it in the context it was written, I can’t take it as certainty.
Also, heat stress is talked about almost in passing. “Heat stress is there, avoid it!” There isn’t any discussion about it or how it’s referenced in the Kunze text.
I’d say that it’s important to remember that not everything that applies at a commercial scale applies at the homebrew level. For example, people worry a lot about fermenter geometry, but when your dealing with 5-10 gallons the pressure at the bottom is negligible, regardless of shape.
